1. Field of the Invention
The present invention relates to a heat medium heating device that heats a heat medium using a PTC heater, and a vehicle air conditioner including the heat medium heating device.
2. Description of Related Art
There is known a heat medium heating device which is provided in a vehicle air conditioner applied to an electric vehicle, a hybrid vehicle, or the like to heat a heated medium serving as a heat source for heating. The heat medium heating device incorporates a PTC heater using a positive characteristic thermistor element (Positive Temperature Coefficient; hereinafter referred to as “PTC element”) as a heat generation element. Japanese Unexamined Patent Application, Publication No. 2008-7106 discloses an example of such a heat medium heating device. The heat medium heating device has a structure in which a number of partitions are provided to partition the inside of a housing including an outlet/inlet path for heat medium into a heating chamber and a heat medium circulation chamber, and PTC heaters are inserted and placed so as to contact the partitions on the heating chamber side to heat the heat medium circulating on the circulation chamber side. Further, a control substrate of each PTC heater is disposed at an upper position thereof.
In addition, Japanese Unexamined Patent Application, Publication No. 2011-16489 discloses a heat medium heating device having a stacked structure in which a pair of heat medium circulating portions are stacked and disposed on both surfaces of each PTC heater so as to sandwich each PTC heater, and a substrate accommodating portion that accommodates a control substrate is provided on one side. Furthermore, Japanese Unexamined Patent Application, Publication No. 2011-79344 discloses a heat medium heating device in which a heat exchange portion provided with a number of flat heat exchange tubes between a pair of headers in a casing including an outlet/inlet path for heat medium; PTC heaters are placed between the flat heat exchange tubes; and a control substrate of each PTC heater is disposed at an upper position thereof.
Thus, the techniques disclosed in Japanese Unexamined Patent Application, Publication Nos. 2008-7106 and 2011-79344 have problems in that it is difficult to bring each partition serving as a heat transfer surface or the flat heat exchange tube into close contact with each PTC heater; and the heat transfer efficiency is reduced, for example. On the other hand, according to the technique disclosed in Japanese Unexamined Patent Application, Publication No. 2011-16489, each PTC heater and each heat medium circulating portion can be stacked to fastened and fixed, thereby increasing the adhesion and reducing the contact thermal resistance. However, it is difficult to dispose a number of PTC heaters in multiple layers, and there are limitations on reduction in size and weight and reduction in costs.
Under such circumstances, the heat medium heating device has been developed in which heat exchange tubes each having a flat structure are used; the flat heat exchange tubes and PTC heaters are stacked in multiple layers to constitute a heat exchange element; the heat exchange element is fastened and fixed to be incorporated into a casing, thereby making it possible to improve the heat transfer efficiency and reduce the size, weight, and costs.